A malewithtrisomy 9mosaicism andmaternal uniparental disomyforchromosome 9inthe euploid cell line

We describe a17yearoldmalewithalow leveloftrisomy9mosaicism. Maternal uniparental chromosome9disomyinthe euploid cell linewasshowntohavearisen afterpostzygotic lossofthepaternal chromosome9fromthetrisomic cell line by cytogenetic andmolecular analysis. Thisisbelieved tobethefirst reportof uniparental disomyforchromosome9. Infourofthe11reportedcasesof mosaictrisomy9 syndrome,including ourpatient, a maternally derived pericentric inversion oftheheterochromatic areaofchromosome9hasbeenpresent induplicate inthetrisomic cell line. This may haveimplications forthecounsellingofpatients withthiscommon chromosomalvariant. (JMedGenet1992;29:742-4) Mosaic trisomy 9syndrome isararecondition withonly11reported cases.' We describe a patient withtrisomy 9 mosaicism anda numberofunusual features.